1. Field of the Invention
The present invention relates to power supply devices, and more particularly, to a power supply device for producing a constant supply voltage on the basis of an externally supplied voltage, a method for controlling the power supply device, and an electronic apparatus incorporating the power supply device.
2. Background Art
Constant-voltage power supplies have been employed in electronic apparatuses, such as cellular phones, smartphones, or portable game players, which run on a small battery. Some constant-voltage power supplies have been suggested which include a first constant-voltage circuit used during a typical operating state (referred to as the active mode), for example, while a call is being made, and a second constant-voltage circuit used during a standby state (referred to as the sleep mode). See, for example, FIG. 1 of Patent Literature 1. Each of these first and second constant-voltage circuits is provided with a reference voltage generation part for producing a reference voltage as a target value of the supply voltage based on a voltage supplied from a battery, and an amplifying part for producing a supply voltage based on the reference voltage. The constant-voltage power supply may be incorporated into a device such as a cellular phone which is actually operated for a longer time in the sleep mode than in the active mode. In this case, power consumption of the aforementioned second constant-voltage circuit responsible for supplying power in the sleep mode can be reduced, thereby reducing the power consumption of the overall system.
In order to implement low power consumption, a drive current to the aforementioned second constant-voltage circuit, particularly, to the reference voltage generation part may be reduced. However, the reduction in the drive current may cause the system significantly affected by variations in the capacity of components constituting the reference voltage generation part and variations of the components' characteristics caused by temperature changes. This leads to degradation in the accuracy of the reference voltage, which will in turn raise the problem that the supply voltage produced in the sleep mode cannot be easily maintained at a desired reference voltage.